This invention relates to a noise-suppressing air intake for ventilation fans, and in particular to such intakes for mine ventilation fans.
Large high speed fans are needed to move the large volume of air required in certain ventilation applications, such as for underground mines. These high speed fans generate blade noise in discrete frequency bands that are proportional to the number of fan blades and the fan speed. In the case of a mine ventilating fan, which runs continuously, the surface noise can be very disturbing to the people living and working nearby.
Most devices for reducing fan noise also reduce air pressure, putting additional load on the fan and requiring more energy to maintain the same flow rate. Thus there are competing considerations between noise reduction and minimizing pressure loss. Noise reduction devices now in use typically provide long tapering air intakes lined with acoustic material. These devices are very large, and consequently very expensive.